Production of methane by bacterial action

ABSTRACT

A mixture of coal and sewage solids is digested by anaerobic bacteria to produce methane.

9 1, Elmte States atent [151 3,640,846

Johnson 1 Feb. 8, 1972 [54] PRODUCTION OF METHANE BY 56] References Cited BACTERIAL ACTION UNITED STATES PATENTS [72] menu: Glen pttsburgh 1,990,523 2/1935 Buswell et al ..195/33 [73] Assignee: The United States of America as represented by the Secretary of the Interi- OTHER PUBLICATIONS 0r Davis, J. B., Petroleum Microbiology, pp 18 5 l ?/lf} /Z [22] $156521 a]:Jam/a1bra /1611mmResearch", v01 58, 21 Appl.No.: 820,328 No. 4, 2/15/39 p.273

Primary ExaminerJoseph M. Golian [52] gig wfz g s 52 5 AttorneyEmest s. Cohen and M. Howard Silverstein 51 1111.121. ..C12d 5/10,c02c 1/14 [58] Field ofSearch ..195/27,2s, 104, 33; 210/1, [57] ABSTRACT A mixture of coal and sewage solids is digested by anaerobic bacteria to produce methane.

1 Claims, N0 Drawings PR D T F METHANE BY BACTERIAL ACTION ticulate coal (e.g., 325 mesh) is preferred since more coal This invention relates to producing methane from coal and Surface i ed, Sewage SOlidS- The following examples illustrate the effect of coal on Most methane used today is obtained from the earth by n robi dig tion. means of gas wells. in some areas and for specific uses, how- 5 ever, methane is manufactured by conventional gasmaking EXAMPLE] processes from both liquid and solid fuels. The sources of Three 2,000 ml. samples of activated sewage sludge which natural gas are limited and the gas is becoming more costly to contained anaerobic methane-producing organisms were recover as deeper wells are of necessity being drilled in more placed in separate glass flasks, from which air had previously inaccessible locations. As a result, the demand for manufacbeen flushed from each flask system with an inert gas (helium tured gas is increasing. or nitrogen). To one of the flasks was added an individual 100 Heretofore, methane has been manufactured by coal cargram sample of LVB coal (-325 mesh); to another, 100 grams bonization techniques such as the Lurgi process and the carof HVAB (325 mesh) coal was added. The third flask conbureted water gas reaction, and by the reforming of liquid fuels such as naphtha. Methane has also been produced, on a tained no coal. The contents ofeachflask was slowly stirred The product gas produced during digestion (at 95 1 00 1 )in smaller scale, during the digestion of sewage by anaerobic each flask was periodically quantitatively and qualitatively bacteria. 7 V I g V analyzed. The results were as follows:

TABLE I Test results with sludge only Test results with LVB coal Test results with H'VAB coal Gas analysis, vol. Gas analysis, vol. Gas analysis, vol.

percent Cumulapercent Cumulapercent Cum ulative gas tive gas tive gas Carbon volume, Carbon volume, Carbon volume, Hours of operation Methane dioxide liters Methane dioxide liters Methane dioxide liters We have now discovered that a mixture of sewage and coal EXAMPLE 2 t' f h Increases the produc 0 met am by anaem Two 2,000 mi. samples of activated sewage sludge which contained anaerobic methane-producing organisms were it is therefore an object of the present invention to produce placed in separate glass flasks from which air had previously methane through anaerobic digestion. Another object is to u employ anaerobic bacteria to produce methane from coal. A been flushed with an men gas (hehum or nmogen) Inma further object is to increase the production of methane from coal was addf'd either flask Lignite was later added to sewage digestion by the addition of coal. Astill further object 40 both flasks at the Show below The Contents of each is to provide additional sewage gas to operate the engines in flask w Slowly z' Procllmt 8 p 'f f during those sewage disposal plants which utilize sewage gas-burning, dlgestlo" 95 00 each flask was Penodlcally q engines. titatively and qualitatively analyzed. The results were as fol- In the practice of the invention a sewage sludge containing lows! v methane-producing anaerobic bacteria is admixed with particulate coal in a vessel from which air is excluded. Since sewage solids decomposition for methane production is best TABLE 2 attained at about 95-100 F., the vessel is preferably main- Test A Test B tained at this temperature, although a wider temperature G 1 C l G 1 C 1 range (e.g., about 50l50 F.) can be employed. Any ii figggg s fi z ggfig a g methane-producing anaerobic bacteria heretofore employed ours of volume, v to produce methane from Sewage can be p y in the operation Methane CO2 liters Methane C02 liters practice of the present invention. A discussion of such 583 Z2 2% 3g -g digestion appears in Biological Waste Treatment by W. W. :1: 52 43 2 90 10 Eckenfelder, Jr. and D. J. OConnor, MacMillan Co., NY. 325 70 30 95 5 400 74 26 4.0 95 5 4.1 1961, pages 248269. Exemplary bacteria suitable for the pur- 500 74 25 5,3 95 5 5 poses of the present invention are found in the genera 58g 2 g f? ig Methanobacterium, Methanococcus and Methanosarcina. 56 44 1 4 "i "ib' 5:4 Suitable coal-to-sludge weight ratios are about 1:100 to about 60 1,100 1:2. Generally, there is no limitation as to the ax 200 g.lignite -325 mesh) added in testAat the end of 100 h0u!S,75O amount of coal that can be added. hours and L030 hours' 1 Gas production in test B ceased after 900 hours; 100 g. lignite (325 Although round-shaped tanks are usually employed to mesh) added at the end of 900 hours which relnitlated gas production produce methane from sewage sludge, the present operation is f minutes- ,7 also readily carried out in rectangular or oblong vessels, either horizontally or vertically disposed, through which the coal and sludge are concurrently fed. EXAMPLE 3 The lower ranking coals such as lignite and subbituminous A, B and C are preferably l d because h contain 3,000 ml. of sewage sludge which contained anaerobic bacmore celluloselike material upon which the bacteria may feed, teria was placed in an air-free flask at 95-l00 F. Product gas However, higher ranking coals such as low volatile bituminous Was periodic lly quantitati e y an qualitatively analyzed.

(LVB) and high volatile A bituminous (HVAB) can be em- After 365 hours when gas production ceased, 250 grams of ployed. Whatever coal is employed, at the termination of gas powdered lignite were added to the flask. The product gas was production the residual coal can be employed as fuel. A coal again qualitatively and quantitatively analyzed.

particle size of about 60 mesh is suitable although finer par- Th results w r as f ll ws:

Gas production ceased after 365 hours; 250 grams of lignite 325 mesh) was then added reinitiating gas production.

As can be seen from Table l, the addition of coal has a pronounced effect on total gas production. The LVB coal more than doubled gas production while the HVAB coal almost achieved the same result. Table 2 shows that lignite also hasa similar effect. Tables 2 and 3 both show that the addition of coal at a point where gas production has ceased will substantially reactivate such production.

At sewage facilities internal combustion engines are generally used to drive auxiliary equipment such as sewage pumps or blowers'which provide air for the aeration tanks, etc. Heretofore, the generation of sewage gas (C0 +Cl-i at such facilities has generally been insufficient to completelyoperate those engines on sewage gas, and the fuel has to be supplemented with natural gas. The present invention provides a method of generating sufiicient gas at such facilities to completely fuel all these auxiliary engines.

' An additional benefit of the present invention is that coal which has been previously used elsewhere in a sewage treatment system as, for example, an adsorbent, settling agent, filter aid, filtration agent or the like, can be reused in the present digestion process to generate gas.

Since coal provides improved methane gas production from sewage digestion, strains of bacteria could probably be developed which feed on coal alone. Such bacteria could then be injected in water which, when flooded into worked-out coal mines, would feed upon coal refuse left underground, and

result in methane production.

What is claimed is:

1. A process for producing methane by the anaerobic digestion of sewage sludge consisting essentially of anaerobically digesting sewage sludge to produce methane; adding coal to said sludge during said digestion step, wherein the coalsludge ratio is 100 grams of coal per 2,000 ml. of said sludge, wherein the temperature during digestion is about -100 F.; and wherein said coal is selected from the group consisting of lignite, subbituminous, and bituminous. 

